The toothed PTO stub shaft and the output shaft of the PTO transmission usually form a shaft-hub connection, the output shaft comprising the recess having the hub function. Shaft-hub connections have long been known in the state of the art and serve for rotationally fixing two shafts together, in order to transmit torques from one shaft to the other. This is a positively interlocking connection, in which torques are transmitted from one shaft to the other by virtue of their mating shapes. Shaft-hub connections are used in motor vehicle transmissions, particularly where shaft connections frequently have to be changed.
On John Deere agricultural tractors in the 5000, 6000 and 7000 series, for example, the rear PTO at the rear of the tractor is designed in such a way that a PTO stub shaft is embodied as a reversible, double-sided shaft. The PTO stub shaft has a 6-tooth profile on a first end area and a 21-tooth profile on another end area. These two profiles are described in relevant standards. The operator can therefore introduce the PTO stub shaft into the PTO with one tooth profile or the other. Different implements, which are each intended for operation at standard speeds (of 540 or 1000 rpm) can therefore easily have their drive shaft adapted to the tractor, the respective drive shaft having a toothing (6 or 21-tooth profile) designed to complement the toothing of the PTO stub shaft. The reversible PTO stub shaft is rotationally fixed by means of drive toothing to the output shaft or PTO of the PTO transmission.
For agricultural machines it is therefore typical to offer different PTO speeds. The following speeds, for example are used as standard: 540 rpm, 1000 rpm, 540E and 1000E. In the case of the 540E and 1000E speeds (E=Economy) the respective speeds 540 rpm and 1000 rpm are substantially available, but the overall gear ratios of the PTO transmission and/or of the vehicle transmission are selected so that the internal combustion engine can in this case be operated at a lower number of revolutions (for example, at just 1700 or 1600 rpm instead of 2100 or 2000 rpm) and can thereby be operated more favorably in terms of fuel consumption. For these different speeds and also power output ranges, the different aforementioned PTO tooth profiles of the transmission output shaft are used, that is to say the 6, 20 or 21-tooth profile. In various regulations and guidelines it is specified, particularly in the USA, that for the 540 and 540E speeds the 6-tooth profile must be available for connection to the implement, whilst for the 1000 (or also the 1000E) speed, use of the 21-tooth profile is obligatory as is the use of a 20-tooth profile for higher power classes. Alternatively the required PTO speed must be automatically limited.
Various systems are known, in which a mechanism of the PTO transmission is automatically shifted by reversing or even changing the PTO stub shaft. This mechanism shifts a gearshift sleeve, for example, in the case of two-speed PTOs, or in the case of three-speed PTOs a lever mechanism is used which, if the 6-tooth profile is projecting, mechanically or electronically prevents the setting for the 1000 rpm speed. The costs of such lever systems are high and the design configuration can be susceptible to malfunction.